I am really interested in Complex Event Processing and have been looking at Esper. However my company has an anti-GPL stance and I was wondering if there are non-GPL alternatives out there under a more business friendly license like Apache or BSD?

Drools Fusion has an ASL-style license (http://legacy.drools.codehaus.org/Licensing). Pion is another open-source system with an AGPL license. If you prefer a normal commercial license there's Aleri, Streambase and ruleCore. Aleri and streambase are "normal" software and ruleCore is a CEP cloud.

If GPL is not-business-friendly, then AGPL is more so. My plain english read of GPL vs AGPL is AGPL prohibits even loose-coupled (not linked) usage of functional with/without an formal API, where the ecosystem is proprietary. Typically when people are looking for business-friendly FOSS, they are basically looking to reap the benefits of open-source without necessarily having to give back any. For all the love-n-affection many corporates show towards Open-source, this is the single biggest motivation, apart from some PR brownie-points.
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icarus74May 25 '11 at 14:56

SiddhiCEP is an Apache License v2 software. You can use that as a library or even as a CEP Server. If you are going for production you can also get production support for SiddhiCEP from the open source product company called WSO2

You might want to take a look at OpenESB's Intelligent Event Processor. I have not looked at it in any detail, but I did find it difficult to determine exactly what the underlying API was. Rather, it talks a lot about a NetBeans IDE that allows you define an event processing work-flow, which is ok, but what I would like to understand better is what the real API is underlying the IDE. In contrast, Esper is all about the API and much lighter on the assistive tools.

I am also not sure what the license is, but I assume that as part of the Sun GlassFish initiative, it would be CDDL (correct acronym ?)

FYI Esper Enterprise Edition does not use the GPL. I.e. no copy left problem...

Can I freely use Esper in my application?

Esper is licensed under the
open source GPL GNU Public License v2.0 license. You may check this
license depending on your application and how you redistribute it.
Restrictions may apply. You should consider Esper Enterprise Edition
for any production use. Esper Enterprise Edition is not made available
under a viral copyleft license and combines Esper, EsperJMX, EsperJDBC
and Esper Studio in one single certified and supported package for
maximal productivity, interoperability and manageability.

The rulecore cep server has a non-gpl (closed) source code license. If you purchase a license from ruleCore, you are allowed to modify the source and distribute your own version without showing your modifies source code to anyone. Might be a good idea for a commercial project with all kinds of IP issues.